Pressing devices or current collectors of this kind are well known in the art and are regularly used on track vehicles for transferring electrical energy from a current rail to the vehicle. The current rail is usually arranged in the vicinity of the driving rails and is often called the third rail. With known current collectors a contact shoe is attached to a rocker wherein the rocker presses the contact shoe with a defined pressing force against a sliding contact surface of the current rail. The contact shoe is brought into contact with the current rail by driving the contact shoe onto the current rail via a starting ramp, wherein the rocker is then pressed back via the contact shoe, thus resulting in the spring unit applying the necessary pressing force.
U.S. Pat. No. 3,740,498 has disclosed such a pressing device, wherein here the spring unit comprises a rubber element. A rotatable rocker unit is designed such that it is able to move a contact shoe unit or a contact shoe up or down between two stops relative to the current rail. The rubber element of the spring unit is rotatably connected with a shaft wherein by rotating and fixing the shaft the rubber element can be tensioned against a stop resulting in the desired pressing force being achieved by forming a sliding contact with the current rail and moving the contact shoe unit or rocker unit against the initial tension.
The disadvantage when using a rubber element as a spring unit consists in that the rubber element loses its spring effect relatively quickly and requires frequent replacement. Furthermore the rubber element is unable to provide for an adequate mounting of the contact shoe unit relative to the current rail. The contact shoe unit can be moved not only up and down but also back and forth in longitudinal direction of the current rail. It is also necessary to pre-tension the rubber element in order to be able to generate an adequate pressing force. It is therefore possible that during operation of the current rail the sliding contact is interrupted if the contact shoe unit moves in an undesirable manner or that a sufficient pressing force fails to be applied upon the current rail.